Merge branch 'ps/reftable-alloc-failures-zalloc-fix'

Recent reftable updates mistook a NULL return from a request for
0-byte allocation as OOM and died unnecessarily, which has been
corrected.

* ps/reftable-alloc-failures-zalloc-fix:
  reftable/basics: return NULL on zero-sized allocations
  reftable/stack: fix zero-sized allocation when there are no readers
  reftable/merged: fix zero-sized allocation when there are no readers
  reftable/stack: don't perform auto-compaction with less than two tables

reftable/basics.c

@@ -17,13 +17,20 @@ static void (*reftable_free_ptr)(void *);
 
 void *reftable_malloc(size_t sz)
 {
+	if (!sz)
+		return NULL;
 	if (reftable_malloc_ptr)
 		return (*reftable_malloc_ptr)(sz);
 	return malloc(sz);
 }
 
 void *reftable_realloc(void *p, size_t sz)
 {
+	if (!sz) {
+		reftable_free(p);
+		return NULL;
+	}
+
 	if (reftable_realloc_ptr)
 		return (*reftable_realloc_ptr)(p, sz);
 	return realloc(p, sz);

reftable/merged.c

@@ -240,14 +240,16 @@ int merged_table_init_iter(struct reftable_merged_table *mt,
 			   struct reftable_iterator *it,
 			   uint8_t typ)
 {
-	struct merged_subiter *subiters;
+	struct merged_subiter *subiters = NULL;
 	struct merged_iter *mi = NULL;
 	int ret;
 
-	REFTABLE_CALLOC_ARRAY(subiters, mt->readers_len);
-	if (!subiters) {
-		ret = REFTABLE_OUT_OF_MEMORY_ERROR;
-		goto out;
+	if (mt->readers_len) {
+		REFTABLE_CALLOC_ARRAY(subiters, mt->readers_len);
+		if (!subiters) {
+			ret = REFTABLE_OUT_OF_MEMORY_ERROR;
+			goto out;
+		}
 	}
 
 	for (size_t i = 0; i < mt->readers_len; i++) {

reftable/stack.c

@@ -270,28 +270,32 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 				      int reuse_open)
 {
 	size_t cur_len = !st->merged ? 0 : st->merged->readers_len;
-	struct reftable_reader **cur;
+	struct reftable_reader **cur = NULL;
 	struct reftable_reader **reused = NULL;
-	struct reftable_reader **new_readers;
+	struct reftable_reader **new_readers = NULL;
 	size_t reused_len = 0, reused_alloc = 0, names_len;
 	size_t new_readers_len = 0;
 	struct reftable_merged_table *new_merged = NULL;
 	struct reftable_buf table_path = REFTABLE_BUF_INIT;
 	int err = 0;
 	size_t i;
 
-	cur = stack_copy_readers(st, cur_len);
-	if (!cur) {
-		err = REFTABLE_OUT_OF_MEMORY_ERROR;
-		goto done;
+	if (cur_len) {
+		cur = stack_copy_readers(st, cur_len);
+		if (!cur) {
+			err = REFTABLE_OUT_OF_MEMORY_ERROR;
+			goto done;
+		}
 	}
 
 	names_len = names_length(names);
 
-	new_readers = reftable_calloc(names_len, sizeof(*new_readers));
-	if (!new_readers) {
-		err = REFTABLE_OUT_OF_MEMORY_ERROR;
-		goto done;
+	if (names_len) {
+		new_readers = reftable_calloc(names_len, sizeof(*new_readers));
+		if (!new_readers) {
+			err = REFTABLE_OUT_OF_MEMORY_ERROR;
+			goto done;
+		}
 	}
 
 	while (*names) {
@@ -1627,6 +1631,9 @@ int reftable_stack_auto_compact(struct reftable_stack *st)
 	struct segment seg;
 	uint64_t *sizes;
 
+	if (st->merged->readers_len < 2)
+		return 0;
+
 	sizes = stack_table_sizes_for_compaction(st);
 	if (!sizes)
 		return REFTABLE_OUT_OF_MEMORY_ERROR;